Introduction Part B. Ultra-efficient Solid-State Lighting: Likely Characteristics, Economic Benefits, Technological Approaches

Technologies for artificial lighting, as illustrated on the left side of Fig. 2.1, have made tremendous progress over the centuries: from fire, with an efficiency of about a tenth of a percent; to incandescent lamps, with an efficiency of about 4 %; to gas discharge lamps, with an efficiency of about 20 %; and soon to solid-state lighting (SSL), with efficiencies that in principle could approach 100 %. At this point in time, there is virtually no question that SSL will eventually displace its predecessor technologies. A remaining question, however, is what the final efficiency of SSL will be. Will it be, as illustrated on the right side of Fig. 2.1, 50 %, which is what the community (Haitz and Tsao in Phys. Status Solidi A 208: 17-29, 2011) has long targeted as its "efficient" lighting goal? Will it be 70 % or higher, which is what some (Phillips et al. in Laser Photon. Rev. 1: 307-333, 2007) have called the "ultra-efficient" lighting goal? Or will it be even beyond an effective efficiency of 100 %, something that might be enabled by smart lighting (Kim and Schubert in Science 308: 1274-1278, 2005), in which one doesn't just engineer the efficiency with which light is produced, but the efficiency with which light is used? In this chapter, we give a perspective on the future of SSL, with a focus on ultrahigh efficiencies. We ask, and sketch answers to, three questions. First, what are some of the likely characteristics of ultra-efficient SSL? Second, what are some of the economic benefits of ultra-efficient SSL? And, third, what are some of the challenges associated with the various technological approaches that could be explored for ultra-efficient SSL?